JP2005303135A - Illuminating optical device, and projective exposure apparatus using same optical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an illuminating optical device having a durability improved by providing in it a highly durable pulse delaying circuit. <P>SOLUTION: In the illuminating optical device for illuminating an illuminated surface by using pulse light having a wavelength not longer than 200 nm which is emitted from a pulse laser, the illuminating optical device includes a pulse delaying circuit for converting the time profile of the pulse light, the pulse delaying circuit splits the pulse light by a beam splitting optical member having a transmitting region and a reflecting region, and the pulse light split respectively by the transmitting region and the reflecting region are synthesized while giving to them a predetermined optical path difference not shorter than the coherence length of the pulse light. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an illumination device that illuminates a surface to be illuminated using light from a light source, and in particular, during a lithography process for manufacturing a semiconductor element, a liquid crystal display element, an imaging element (CCD, etc.), a thin film magnetic head, or the like. The present invention relates to an illumination apparatus that illuminates a mask on which a pattern is drawn in a projection exposure apparatus used in the above-described field.

  An exposure apparatus is used in the lithography process of the semiconductor element manufacturing process. The lithography process is a process of projecting and transferring a circuit pattern of a semiconductor element onto a substrate (such as a silicon substrate) that becomes a semiconductor element. In recent years, the demand for miniaturization of semiconductor elements has been increasing, and the minimum line width of the line-and-space is about 0.15 μm and is about to reach 0.10 μm. In order to achieve miniaturization, improvement of the resolving power of a projection exposure apparatus used in a lithography process has become a major issue in recent years.

  In general, the resolvable line width R in the lithography process is determined by using the wavelength λ of the exposure light source, the numerical aperture NA of the exposure apparatus, and the proportional constant k1.

Can be written. That is, if the wavelength λ is shortened, the resolvable line width decreases in proportion to the wavelength, and if the numerical aperture NA is increased, the resolvable line width decreases in inverse proportion.

  On the other hand, the defocus tolerance that falls within the allowable line width error in the process is called DOF.

Can be written. That is, if the wavelength is shortened, the defocus tolerance is reduced in proportion to the wavelength, and if the numerical aperture is increased, the defocus tolerance is reduced in inverse proportion to the square.

  That is, as a method of miniaturizing a semiconductor element, there are a method of shortening an exposure wavelength and a method of increasing the numerical aperture of an exposure apparatus. To achieve miniaturization while taking as much defocus tolerance as possible, NA It is more desirable to shorten the exposure wavelength than to increase For this reason, in recent years, development of an exposure apparatus in which the wavelength of the exposure light source is shortened has been accelerated. At present, the exposure light source of the mainstream exposure apparatus is a KrF excimer laser with a wavelength of 248 nm. Development is also being done.

  However, a new problem has arisen with the shortening of the wavelength of the light source. The problem is that the energy of photons (photons) increases, so that damage to the optical member due to light irradiation increases. Damage to the optical member causes a decrease in the transmittance of the glass material, a change in refractive index (compaction), a decrease in the transmittance of the antireflection coating, a decrease in the reflectance of the reflection mirror, etc. Deterioration of imaging performance of the projection optical system due to generation of aberrations in the projection optical system is caused.

  In order to solve such problems, a method called a pulse delay circuit is proposed in which an illumination system is provided with an optical system that artificially extends the emission time of pulsed light and lowers the pulse intensity applied to the optical system. (For example, refer to Patent Document 1).

The prior art will be described with reference to FIG. Reference numeral 1 denotes a laser that oscillates pulsed light, and a KrF excimer laser, an ArF excimer laser, an F2 laser, or the like is used. Reference numeral 6 denotes a half mirror formed of a dielectric multilayer film, which branches light into transmitted light and reflected light at a desired ratio. The beam splitting method is a so-called amplitude division type in which one light beam is divided into two light beams of transmitted light and reflected light. For example, φ (z, t) = A × exp (2πi (νt−z / λ) ), When light having a wavelength λ, a frequency ν, and an amplitude A is incident, transmitted light φ _T (z, t) = B × exp (2πi (νt−z / λ)) and φ _R (z , T) = C × exp (2πi (νt−z / λ)). If the half mirror formed of the dielectric multilayer film has no absorption and all incident light is reflected or transmitted, the relationship A = B + C is established.

  The transmitted light that has passed through the half mirror 6 is directly guided to the illumination optical system 5 and becomes light that illuminates the surface to be illuminated. The reflected light reflected by the half mirror 6 passes through the predetermined optical path length of the optical delay optical system composed of the mirror 8 and the lens 7 and enters the half mirror 6 again. In the half mirror of No. 6, the reflected light and the transmitted light are branched again. The reflected light is guided to the illumination optical system of No. 5, and given a predetermined optical path difference from the light previously guided to the illumination optical system. The light to illuminate the illuminated surface. The light that has passed through the half mirror enters the optical delay optical system again, and then enters the half mirror again through a predetermined optical path length.

One pulse of the pulsed light emitted from the laser is branched as described above and combined with an optical path length difference, so that it apparently enters the illumination optical system as pulsed light of a plurality of pulses. Since the speed of light is approximately 3 × 10 ⁸ m / s, for example, in order to delay 40 ns light, an optical path difference of 12 m may be provided.

  An example of the illumination system 5 is shown in FIG. 1 is a laser as a light source, and 9 is the above-described pulse stretcher. Reference numeral 10 denotes an ND filter for adjusting the illuminance of the surface to be illuminated, and the transmittance can be adjusted discretely or continuously. Reference numeral 11 denotes a first-stage fly-eye lens, which superimposes the light wave-divided by a plurality of rod lenses on the incident surface of the second-stage fly-eye lens using 13 condenser lenses. Thus, the incident surface of the 13th stage fly-eye lens is illuminated substantially uniformly. The wavefront is again divided by a plurality of rod lenses with 13 second-stage flies, and is superimposed on 15 diaphragm surfaces through 14 condenser lenses. By doing so, even if the laser profile changes over time or vibration occurs between the apparatus and the laser, a uniform illuminance distribution is formed on the 15 diaphragm surfaces. The aperture of 15 is an aperture for cutting out the effective light source shape. The cross-sectional shape of the rod lens constituting the thirteenth fly-eye lens is a quadrangle or hexagon, and correspondingly, the illuminance distribution on the fifteen stop is also a square or hexagon. Since the effective light source shape, which is the angular distribution of the illumination light that illuminates the reticle, has a good round shape, light is cut into a circle with 15 stops in order to make the effective light source shape a round shape.

  Reference numeral 16 denotes a relay zoom optical system, which projects uniform light cut out by a stop of 15 onto a third stage fly-eye lens of 17 with variable magnification. In the projection exposure apparatus, the resolution and depth of focus change by changing the effective light source shape. For example, with a simple line and space pattern, the effective light source shape is reduced, the light that illuminates the reticle surface is made close to parallel light, and the resolution is improved by using a reticle called a phase shift mask. Expands.

  The light is again divided into wavefronts by 17 third-stage flies, and projected onto 19 slits by 18 condenser lenses. Thereby, a uniform illuminance distribution is formed on a plane conjugate with the surface to be illuminated. Reference numeral 19 denotes a slit which defines the slit width in the scanning direction of the projection optical system. Changing the slit width in a direction perpendicular to the scanning direction to correct uneven illuminance is also performed. Reference numeral 20 denotes a traveling masking blade that defines an exposure area on the substrate. The traveling masking blade is scanned in synchronism with a reticle and wafer described later.

  Reference numeral 21 denotes a relay optical system, which projects 20 traveling masking blades onto 22 reticles. Reference numeral 22 denotes a reticle on which a pattern is drawn. A part of the reticle, which is an illumination area, is illuminated by the illumination system, scanned in an illuminated state, and the exposure area of the reticle is exposed. A projection lens 23 projects the illuminated reticle region onto a wafer coated with 24 photosensitive agents. The 24 wafers, 22 reticles, and 20 travel masking blades are synchronously scanned to expose the exposure area.

By using the illumination optical system including the pulse delay circuit as described above, one pulse of light is dispersed into a plurality of pulses and enters the illumination optical system, so that the pulse intensity applied to the optical system can be reduced. A method for reducing damage to the system has been proposed.
Japanese Patent Laid-Open No. 9-288251

  In the prior art, in order to branch light in a pulse delay circuit, a half mirror whose transmittance and reflectance are adjusted by a dielectric multilayer film is used. However, when the optical durability of the dielectric multilayer film was performed, the absorption rate by the film increased by 5% by irradiating the light of wavelength 157 nm with the intensity of 10 mJ / cm 2 and 200 mega (1E + 6) pulse, and the transmittance I understood that changed. Since the exposure apparatus emits several virion (1E + 9) pulses in one year, it has been found that the half mirror made of a dielectric multilayer film cannot withstand use in the exposure apparatus because of the increase in the absorption rate. That is, in the prior art, there is a problem that the pulse delay circuit for increasing the durability of the optical system is not durable and the durability of the entire lighting device is low.

  In view of the above, an object of the present invention is to provide a highly durable lighting device including a pulse delay circuit having high durability.

  In order to achieve the above object, an illumination optical apparatus according to one aspect of the present invention is an illumination optical apparatus that illuminates a surface to be illuminated using pulsed light having a wavelength of 200 nm or less emitted from a pulse laser. Including a pulse delay circuit that converts a temporal profile of the pulsed light, the pulse delay circuit branching the pulsed light by an optical branching optical member having a transmission region and a reflection region, and splitting the light branched by the transmission region and the reflection region The present invention is characterized in that a composition is made by adding a predetermined optical path difference equal to or greater than the coherence distance.

  Further objects and other features of the present invention will be made clear by the preferred embodiments described below with reference to the accompanying drawings.

  By using a wavefront splitting optical branching optical element consisting of a highly durable total reflection film for the optical branching optical element of the pulse delay circuit, a highly durable pulse delay circuit that reduces the pulse intensity of the pulsed light is obtained. Therefore, a highly durable illumination optical device and a projection optical system with little change in optical performance can be obtained.

  According to our durability results, it was found that the total reflection film has high durability against irradiation with light having a wavelength of 157 nm. This is because the increase in the absorption rate due to durability occurs at the interface between the film and the glass material. In the case of a half mirror, the transmitted light acts on the interface and the absorption rate increases. In this case, since the light does not reach the interface, the absorption rate does not increase.

  However, at a short wavelength such as 157 nm, since there are few film materials that can be used, it is difficult to produce a total reflection film that is completely reflective only with a dielectric multilayer film. In the present invention, what is called a total reflection film is a metal reflection film such as aluminum or a high reflection film having a transmittance of less than 10% of a dielectric multilayer reflection film.

  In the present invention, based on this durability result, instead of dividing the amplitude of light with a half mirror made of a dielectric multilayer film, the light is divided into wavefronts by an optical member in which a transmission region and a reflection region are arranged. An illumination optical device having a highly durable pulse delay circuit is provided by branching light and forming a pulse delay circuit.

  Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

  A first embodiment of the present invention will be described with reference to FIG.

Reference numeral 1 denotes a laser that oscillates pulsed light, and a KrF excimer laser, an ArF excimer laser, an F2 laser, or the like is used. Reference numeral 2 denotes a wavefront division type optical branching optical member. FIG. 2 shows details of the wavefront division type optical branching optical member 2. The left figure of FIG. 2 is the figure which looked at the wavefront division type | mold optical branching optical member from the front. The filled area in the figure is a reflection area, and the unfilled area is a transmission area. The method of splitting the light beam is either transmitted light or reflected light depending on where one light beam is incident, so-called wavefront split type that splits a light beam with a certain thickness into two light beams It is a branching method called. For example, assuming that a light beam having a wavelength λ, a frequency ν, and an amplitude A, which is written as φ (z, t) = A × exp (2πi (νt−z / λ)), φ _T (z, t) = Axexp (2πi (νt−z / λ)) or reflected light of φ _R (z, t) = A × exp (2πi (νt−z / λ)) Is done.

  The transmission area and the reflection area of the wavefront splitting optical branching optical member are repeatedly arranged at a predetermined period. In order to substantially alleviate the pulse intensity of the light beam branched by the wavefront splitting type optical branching optical member, it is necessary to finely split the laser beam into wavefronts. This is because the light branched by the wavefront splitting optical branching optical member is only branched for each location as described above. This is because the pulse intensity is not relaxed. For example, the pulse intensity for an optical member arranged at a conjugate location is different only in the time when the pulse light hits a portion conjugate with the transmission region and the time when the pulse light hits a conjugate region with the reflection region. The pulse intensity at each point is not relaxed. By defocusing from the conjugate plane, the light beam passing through the transmission region and the light beam reflected by the reflection region are mixed, and the pulse intensity at each point of the optical member can be substantially reduced. The amount of defocus required to mix the light transmitted through the transmissive area and the light reflected from the reflective area becomes smaller as the repetition period of the transmissive area and the reflective area becomes smaller. More members.

  However, on the other hand, if the repetition period is made too small, the wavefront splitting optical branching optical element will function notably as a diffractive optical element, and the diffracted light will jump out of the effective diameter of the illumination optical system, reducing the light utilization efficiency. End up. The diffraction angle of the diffracted light is an angle θ that satisfies λ = d × sin θ. λ is the wavelength of light, and d is the repetition period of the diffractive optical element. When the diffraction angle is 1 degree or more, the light kicked by the illumination optical system cannot be ignored. Therefore, when the wavelength of light is 157 nm, the light can be branched without deteriorating the light utilization efficiency by setting the repetition period of the diffractive optical element to 9 μm or more.

  The transmittance and reflectance of the wavefront splitting optical branching optical element can be adjusted by changing the area ratio of the reflective region to the transmissive region. For example, it is repeatedly arranged one-dimensionally with a repetition period of 100 μm shown in FIG. In the wavefront splitting optical branching optical element, when the transmittance is 30% and the reflectance is 70%, the width of the transmissive region may be 30 μm and the width of the reflective region may be 70 μm. In the example of FIG. 2, the example in which the transmission region and the reflection region are repeatedly arranged in one dimension is shown. However, as shown in FIG. 6, the transmission region and the reflection region are randomly arranged as shown in a checkered pattern, a dot shape, or the like. However, the reflective area and the transmissive area may have a predetermined area ratio as a whole.

  The transmitted light that has passed through the wavefront division type optical branching optical element 2 is directly guided to the illumination optical system 5 and becomes light that illuminates the illuminated surface. The reflected light reflected by the two wavefront splitting optical branching optical elements is incident again on the two wavefront splitting optical branching optical elements through a predetermined optical path length of an optical delay optical system composed of 3 and 4 spherical mirrors. The optical delay optical system consisting of 3 and 4 is an imaging system in which aberrations are sufficiently removed. If the light reflected from the reflection region returns to the reflection region, the two wavefront division type optical branching optical members can be obtained. The re-incident light is reflected and guided to the illumination optical system 5, and becomes a light that illuminates the illuminated surface with a predetermined optical path difference from the light previously guided to the illumination optical system. . In order to return from the reflection area to the reflection area, since the wavefront division type optical member has a thickness, a mirror imaging system including eccentricity is used, or a parallel plate having the same thickness as the wavefront division type optical member is inserted. It is necessary to arrange so as to cancel the shift, or to arrange the repetitive direction of the reflection area and the transmission area perpendicular to the shift direction.

One pulse of the pulsed light emitted from the laser is branched as described above and combined with an optical path length difference, so that it apparently enters the illumination optical system as pulsed light of a plurality of pulses. Since the speed of light is approximately 3 × 10 ⁸ m / s, for example, in order to delay 40 ns light, an optical path difference of 12 m may be provided.

  Any illumination optical system 5 may be provided. For example, the illumination optical system described in the conventional example of FIG. 4 is used.

  As described above, the durability of the pulse delay circuit can be improved by using the optical branching optical member using the highly durable total reflection film, and one pulse of light is dispersed into a plurality of pulses. Since the incident light is incident on the illumination optical system, the pulse intensity applied to the optical system can be lowered. Therefore, it is possible to provide a highly durable illumination optical apparatus and an exposure apparatus with little change in optical performance.

  A second embodiment of the present invention will be described with reference to FIG. The difference between the second embodiment and the first embodiment is only the configuration of the wavefront splitting optical branching optical element, and the other portions are the same as those of the first embodiment. In the first embodiment, the light reflected from the first surface of the light branching element is configured to enter the second surface and reflect the light from the first surface through an optical delay circuit. In this case, since the light entering from the second surface passes through the interface between the film on the first surface and the glass material, there is a possibility that the absorption rate is increased due to the durability of the interface. The second embodiment is for solving the above-mentioned problem. As shown in FIG. 5, a reflection region and a transmission region are further arranged on the second surface, and the light passing through the pulse delay circuit is second. The light is reflected by a reflective film formed on the surface.

  The light transmitted from the second surface is transmitted through the second surface so that the light transmitted from the first surface is transmitted through the second surface with the arrangement of the transmission region and the reflection region of the first surface and the second surface tilted. It arrange | positions so that the 1st surface may be permeate | transmitted. As described above, since the light does not reach the interface of the total reflection film, the durability of the reflection film can be improved, and the illumination optical device having the highly durable pulse delay circuit and the optical performance change Fewer exposure apparatuses can be provided.

  In the first and second embodiments, the optical delay optical system is an imaging system with sufficient aberrations. In the third embodiment, a predetermined blur amount is given to the imaging system, or The light reflected by the reflection region of the wavefront splitting optical branching optical element is passed through the delay optical system and shifted by a predetermined amount by using a parallel plate or an eccentric imaging system. Not only the reflection area but also the transmission area. As a result, the light that has returned to the wavefront splitting optical branching optical element is split again into reflected light and transmitted light. Therefore, in the first and second embodiments, one pulse of light is split into only two pulses. However, in the third embodiment, one pulse of light is divided into a plurality of pulses. If the transmittance of the pulse delay circuit is 100% and the absorption factor of the optical branching optical element is 0, it is divided into infinite pulses, but actually the transmittance of the pulse delay circuit is not 100%, and the optical branching optics Since the absorptance of the element is not 0, it is effectively divided into 3 to 5 pulses. Thereby, the pulse intensity to the optical system can be lowered as compared with the first and second embodiments.

  Next, an embodiment of a device manufacturing method using the above exposure apparatus will be described.

  FIG. 7 shows a manufacturing flow of a semiconductor device (a semiconductor chip such as an IC or LSI, a liquid crystal panel or a CCD). In step 1 (circuit design), the circuit of the semiconductor device is designed. In step 2 (mask production), a mask (reticle) on which the designed circuit pattern is formed is produced. On the other hand, in step 3 (wafer manufacture), a wafer is manufactured using a material such as silicon. Step 4 (wafer process) is called a pre-process, and an actual circuit is formed on the wafer by lithography using the prepared mask and wafer. The next step 5 (assembly) is called a post-process, and is a process for forming a chip using the wafer created in step 4, and the assembly process (dicing, bonding), packaging process (chip encapsulation) and the like are performed. Including. In step 6 (inspection), inspections such as an operation confirmation test and a durability test of the semiconductor device created in step 5 are performed. Through these steps, the semiconductor device is completed and shipped (step 7).

  FIG. 8 shows a detailed flow of the wafer process. In step 11 (oxidation), the wafer surface is oxidized. In step 12, an insulating film is formed on the surface of the wafer. In step 13 (electrode formation), an electrode is formed on the wafer by vapor deposition. In step 14 (ion implantation), ions are implanted into the wafer. In step 15 (resist process), a resist (sensitive material) is applied to the wafer. In step 16 (exposure), the wafer is exposed with an image of the circuit pattern of the mask by the exposure apparatus described above. In step 17 (development), the exposed wafer is developed. In step 18 (etching), portions other than the developed resist are removed. In step 19 (resist stripping), unnecessary resist after etching is removed. By repeating these steps, a circuit pattern is formed on the wafer.

  By using the manufacturing method of this embodiment, it becomes possible to manufacture a highly integrated device, which has been difficult in the past.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the gist.

It is a figure showing the 1st Example of this invention. It is a figure showing the 1st Example of the wavefront division type optical branching optical member of the present invention. It is a figure showing a prior art example. It is a figure showing the Example of an illumination optical system. It is a figure showing the 2nd Example of the wavefront division type | formula optical branching optical member of this invention. It is a figure showing the example of arrangement | positioning of the reflective area | region of a wavefront division type | mold optical branching optical element, and a permeation | transmission area | region. It is a figure which shows the manufacturing flow of a device. It is a figure which shows the wafer process of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser 2 Wave-front splitting-type optical branching optical member 3 Concave mirror 4 Concave mirror 5 Illumination optical system 6 Dielectric multilayer half mirror 7 Lens 8 Planar mirror 9 Pulse delay circuit 10 Filter 11 Hayeno-eye lens 12 Condenser lens 13 Hayeno-eye lens 14 Condenser lens 15 Aperture 16 Relay zoom optical system 17 Hayeno eye lens 18 Condenser lens 19 Slit 20 Travel masking blade 21 Relay optical system 22 Reticle 23 Projection optical system 24 Wafer

Claims (5)

  An illumination optical apparatus that illuminates a surface to be illuminated with pulsed light having a wavelength of 200 nm or less emitted from a pulse laser, the illumination optical apparatus includes a pulse delay circuit that converts a temporal profile of the pulsed light, and the pulse delay circuit includes The light splitting optical member having a transmission region and a reflection region branches the pulse light, and the light branched in the transmission region and the reflection region is combined with a predetermined optical path difference equal to or greater than the coherence distance. An illumination optical device.   The illumination optical device according to claim 1, wherein a repetition period of the transmission region and the reflection region of the light branching optical member is 9 μm or more.   The pulse delay circuit retransmits transmitted light or reflected light branched by the light branching optical member through a mirror imaging system at a position of the light branching optical member through a predetermined optical path length equal to or greater than a coherent distance. The illumination optical apparatus according to claim 1, wherein the illumination optical apparatus is configured to form an image and combine the images.   In a projection exposure apparatus comprising: an illumination optical apparatus that illuminates a reticle surface on which a pattern is drawn with light emitted from a laser; and a projection optical apparatus that projects a reticle pattern onto a substrate coated with a photosensitive agent. 4. The projection exposure apparatus according to claim 1, wherein the illumination optical apparatus is one of claims 1 to 3.   A device manufacturing method comprising: exposing a substrate using the projection exposure apparatus according to claim 4; and developing the exposed substrate.

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